An Ear for Science: The Particle Physics Windchime

By Lori Ann White
June 23, 2011

Stanford physicist Matt Bellis deals in the infinitesimal. As a member of the BaBar collaboration based at SLAC, he studies what happens when an electron and a positron collide at certain energies. Electrons and positrons have opposite electrical charges, but in all other respects – including mass – they are exactly the same, and they are very small.

As a result, Bellis inhabits a world of visualizations.  Animations, graphs, computer-drawn images, Bellis uses them all to try to picture the scene when a particle that weighs about 9x10^-31 kg – that’s a nine multiplied by a zero-point-thirty more zeros and a 1 – slams into another particle exactly the same size. Granted, in a realm where mass and energy intertwine the particles travel at speeds that give them a little more oomph, but that doesn't change the fact that no one will ever actually see this – except through the magic of special effects. 

Like particle physicists the world over, Bellis is forced to improvise ways to share his research with the public, using whatever  comes to hand. He's animated bristling spheres of particle tracks in sophisticated vector graphics – complete with cool soundtracks. He's illustrated fundamental relationships between different particle types with Google Docs. Bellis has developed a whole toolbox of methods to help him explain particle physics. Until recently, however, all the tools in his toolbox were visual.

A trained musician, Bellis came up with the idea of rendering the results of particle collisions as sounds. The process of rendering data into sound is known in general as "sonification." Bellis wanted to sonify data from BaBar.

"I had the idea of the BaBar detector as an instrument," Bellis said, but not one played by human hands. It would be played by the particles gusting through it, like wind through a wind chime. 

"Think of it," Bellis said.  "The wind itself makes no sound. You hear the wind if it rustles the leaves in a tree. The motion of the wind itself doesn't necessarily make a sound. The wind has to interact with something to make noise." In the same way, "When you have these particles that pass through the detector, they send it ringing, resonating in some way."

Thus was born the idea of the Particle Physics Windchime: A computer application that could take particle physics data such as particle type, momentum, distance from a fixed point, and so on, and turn it into sound. 

Last November, at the urging of ex-SLACer and event co-organizer David Harris, Bellis took his idea to Science Hack Day SF [http://sciencehackday.com/], where enthusiastic programmers, web designers, science fans and self-professed geeks gathered for the express purpose of spending 24 intense hours "hacking together" the basics of several science-related computer applications.

Bellis rounded up an interested group of Science Hack Day attendees, laid his idea before them, and turned them loose on simulated BaBar data. That weekend, they developed the kernel of the Particle Physics Windchime. According to Bellis, his cadre of coders – not all of whom had a background in science – got swept up in the physics of the colliding particles and how to portray them, sonically speaking. By the time the group presented Version 0.1 of the Particle Physics Windchime, they could define some simple relationships such as the energy of a particle to the volume of the sound representing it, or the angle of a particle track to the original electron-positron beam with the pitch of the sound representing the particle.

"We actually won the People's Choice Award" at Science Hack Day, Bellis said, along with the award for Best Use of Data. But what Bellis said he found most interesting about the experience is how involved his team became in particle physics during the course of building the Windchime, and the interest shown by the audience during his team's final presentation.

"I wanted to create the Particle Physics Windchime partly because I thought it was a cool idea, and partly because I wanted to see if there's something new we can learn from the data," Bellis said. "Is there something I can hear in the data that I can't see or that a computer can't pick up? Will it add to an intuitive understanding of the data?" While at Science Hack Day he learned that other particle physicists were thinking along much the same lines – members of the ATLAS group at the Large Hadron Collider had been sonifying LHC data, with the results available on the LHCsound website. All this served to bolster his belief that a sound-based teaching tool could help interest a lay audience in particle physics.

"Science should be something society is involved in," he said. For example, the project he's working on, BaBar, investigated a fundamental imbalance in the way the universe works – the triumph of matter over antimatter. The implications of this imbalance “are so profound that particle physics cannot be just for particle physicists,” Bellis said. “This cannot be just for a few thousand people to understand. We have to find ways to explain it to anybody who wants to know what we're doing, no matter how obscure, no matter how difficult.”

This responsibility is not news to the BaBar collaboration. Now that data-taking is over and collaboration members are busy crunching numbers, an effort to preserve the data for future users is under way, Bellis said. "One of the arguments for preserving well-understood data sets is using them for education and outreach," he explained. "Kindergarten through 12, college, training new people." But he readily admits that explaining even well-understood particle physics data is hard. According to Bellis, he thinks particle physicists may be able to use the Windchime to learn about communicating with the public.

The path from idea to reality has not always been smooth. The demands of research leave Bellis little time to continue developing the Windchime, and to progress to the point of having a robust, easily-customized tool that anyone could play with will take time and resources Bellis currently doesn't have. One option he'd like to try is continuing with the collaborative model of Science Hack Day, in a sense.  "I welcome people who are interested to pitch in," Bellis said. Even if the particle physics doesn't sink in, just working on the Windchime would be educational. "This is a killer app for all ages to learn programming."

In the meantime, Bellis will continue to tinker with the Windchime as time allows. He said he's also eager to introduce it to audiences of all types. And when Bellis says "all types," he means it:  "If I get a gig at a coffeehouse somewhere where I play B-meson music out to a crowd, I will consider this all a success."

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Matt Bellis with the Particle Physics Windchime in the background (Photo by Brad Plummer.)
Matt Bellis stands in front of a projected image from his Particle Physics Windchime, to which he has added visualization capabilities. (Photo by Brad Plummer.)